One additional note is that it's not too uncommon to create custom moves for monsters that are triggered by things that happen in the fiction when engaging with those monsters. Custom "pick a negative consequence from a list" moves can be fun to engage with mechanically. This can work especially well for monsters associated with a Danger Front. It's important to remember though that monsters don't 'do these moves', but rather these moves have triggers in the fiction related to things the monsters do.

One thought is that if you're going to go way off-system (which can be challenging to keep 'balanced' and fun), you might want to just consider a different system. There are a bunch of different systems available with varying levels of crunch and flexibility and some of the more flexible ones can handle things like wanting to be a skeleton necromancer without too much difficulty or rebalancing required. You can certainly have fun hacking DND-5E, but it has a lot of moving parts and it's easy to end up breaking things pretty badly.

While it's okay to discuss moves and mechanics during play, I think it's a good idea to encourage not always explicitly calling out the desired move. Explicit call-outs cultivate a sense of constraint where players think "okay, what move do I want to make now?" Sometimes that's helpful as inspiration for what to do, but there's quite a lot of gameplay and storytelling that can happen without triggering player moves at all.

I'd argue that in Dungeon World (and PbtA in general), descriptions can (and should) usually be part of GM moves. Moves triggered by player character actions are part of the game mechanics, but arguably the GM moves (in the context of the Agenda and Principles) are the more critical mechanic, even if it's not as immediately visible to the players. You're not describing for its sake, but in the service of portraying a fantastic world and filling the characters' lives with adventure. The GM moves give you a framework for shaping that description toward a call to action, moving play forward.

@SouthpawHare, I probably highlighted that part of it a bit too strongly; the answer to the question of what effect happens is tied in with the fiction of how the ability works, just like the question of whether it triggers at all. The main point here is that the rules don't define what happens in these boundary cases, but the fiction does. The fact that the move might not trigger at all is just a way to highlight how differing interpretations of the power behind the move can shape how it functions.